Vapor intrusion, sometimes called subsurface vapor intrusion, occurs when there is a migration of volatile chemicals from contaminated groundwater or soil into an overlying building. Volatile chemicals may migrate through subsurface soils and into indoor air spaces of overlying buildings in ways similar to that of radon gas seeping into homes. Notoriously, many compounds are able to diffuse easily through concrete and other construction materials used in e.g. building foundations. The compounds can accumulate within the interior space of the building, giving rise to actual or potential health risks to building occupants.
For these reasons, measurement of vapor intrusion has become an important environmental topic. Vapor sampling of soil gas and air provides a direct measurement of compounds both beneath and within a building in order to evaluate health risks. However, the actual flux of compounds through the building slab itself can only be inferred by these measurements. Numerous published procedures and guidance documents discuss air and soil gas sampling techniques, sample analysis, and interpretation of data. Most of these publications discuss well-known active vapor sampling techniques. These methods forcefully or mechanically extract a known volume of vapor, which is hopefully a representative sample, from the soil pore space or from free air (e.g., indoor air), and are analyzed on-site or at fixed off-site laboratories following a variety of accepted sampling and analytical methods.
While passive vapor sampling is known, there is a paucity of information on passive methods to obtain accurate measurements in a vapor intrusion application. While some passive vapor sampling devices are known, they tend to be complicated, must be assembled on site from multiple components, and must be carefully situated in an attempt to avoid contamination from non-target sources which destroys the accuracy of the test.
Passive vapor sampling for clothing is known; see e.g. U.S. Pat. No. 5,726,068 describing pouch-like vapor detecting devices. Such devices will not work in a vapor intrusion application—that is, where vapors issuing from the ground must be quantified and separated from ambient vapors present in a building or other space arising from sources other than the ground. This is because the clothing-bound pouch devices measure compounds that arrive via diffusion of ambient air. Such a device does not differentiate volatiles issuing from the ground from those arising from other sources.
An exemplary type of passive sampling device specifically for vapor intrusion is described in U.S. Pat. No. 6,018,981. A rigid, dome shaped cover includes a weighted ring that is placed around the dome to hold the dome against a floor. A container of absorptive material is placed under the dome to absorb vapors. While in theory such an arrangement may work to accurately measure vapors issuing only from the ground, an uneven floor destroys the usefulness of such a device: if the rigid dome is not completely seated (sealed) against the floor, ambient air will leak into the dome. Such leakage destroys the accuracy of any measurement of vapors obtained from the absorbent. Since many concrete floors are less than perfectly planar, such a device has extremely limited utility. Additionally, multiple equipment components are required to assemble the sampling device, which complicates its use.
U.S. Pat. No. 6,018,981 illustrates the challenge in designing passive vapor intrusion devices. Specifically, such devices must accurately measure vapors issuing only from the ground, and must exclude ambient vapors arising from other sources, such as vapors previously issued and present in the atmosphere proximal to the device. While a passive measuring device may be placed subsurface to effectively eliminate above-ground ambient vapors, such an approach is not always possible or practical. Surface contact devices are needed in such applications. We are unaware of any passive vapor intrusion surface devices or methods that completely exclude measurement of ambient vapor sources in practical, real world situations where imperfect exclusion of ambient vapors may be operative.
Thus, there is a need in the industry for a passive vapor sampling device that accurately and repeatably measures vapor intrusion for a range of compounds, including volatile, organic and non-organic compounds, and under a wide range of site conditions. There is a need in the industry for devices, methods of deployment thereof, and analytical measurements taken therefrom that are simple to use, repeatable, accurate, and inexpensive to obtain. There is a need in the industry for a passive vapor intrusion device and method of vapor intrusion quantification that excludes the contribution of ambient vapors in the quantification of vapor intrusion.